This invention relates to insoluble anodes for producing electrolytic manganese dioxide.
Electrolytic manganese dioxide is used chiefly as the active material of dry cells or batteries. This manganese dioxide is usually manufactured by electrolysis from an aqueous sulfuric acid-manganese sulfate solution containing from 0.5 to 1.0 mole manganese sulfate and from 0.2 to 0.6 mole free sulfuric acid per liter of the solution.
The aqueous solution upon electrolysis with a direct current on the order of 0.8 A/cm.sup.2 deposits manganese dioxide on the anode. Once the deposit has built up to a certain extent, it is peeled off and collected as product manganese dioxide. During the process, hydrogen evolves from the cathode.
Titanium has recently come into use as the anode material for the manufacture of electrolytic manganese dioxide. The reason is that the titanium electrode has outstanding corrosion resistance, specific strength, and workability and also precludes anode-induced contamination of electrolytic manganese dioxide and yields a high quality product.
One problem associated with the use of titanium as the anode for the above process has been the growth of the passive state film on the surface with the increase in current density; it raises the bath voltage accordingly, until the flow of current becomes no longer possible. To avoid this problem, it has been necessary to keep the current density within the range around 0.8 A/dm.sup.2.
Current density, thus, has a direct bearing upon productivity in the electrolysis industry. The electrolytic cell employed being the same, the higher the current density the larger would be the scale of production that is made feasible. Also, the output being the same, the electrolytic cell could be made smaller in size as the current density increases, reducing the investment in the electrolytic cell to an economical advantage.
Titanium is used as anodes not merely for the production of electrolytic manganese dioxide but also for other applications. With the latter, too, the difficulty is that increased current density induces the growth of a passive state film on the surface with eventual interruption of current flow. To avoid this, modern practice favors plating of the anodes with a noble metal such as platinum.
However, the plating treatment using an expensive noble metal casts a heavy financial burden on the manufacturer. It, thus, presents a major obstacle in the way of the extensive commercial acceptance of the plated anodes.
With these in view, this invention is aimed at providing at low cost a titanium alloy anode which can replace existing titanium anodes and is characterized by the capability of carrying a greater current density.